EFFECT OF SULFUR DOPING ON ELECTRICAL-CONDUCTIVITY OF A-SI-H

The present paper reports the electrical conductivity and optical band gap measurements of a-Si,S:H films in the alloy range (S/Si ratio 0.51 10(-2) to 4.07*10(-2)) as a function of deposition temperature. The a -Si,S:H samples were prepared by conventional plasma-assisted CVD thro ugh decomposition of H2S and SiH4 mixtures using substrate temperature s up to 500 degrees C. When the deposition temperature is raised From 230 tu 500 degrees C, the concentration of S in the films decreases. T he main effect of S alloying is a strong increase in IR mode at approx imately 480 cm(-1) which corresponds to Si-S bond. The optical bandgap decreases dramatically with deposition temperature. The conductivity is found to be activated with the fermi level moving towards the condu ction band edge up to S/Si ratio of 0.51 10(-2) and as the S/Si rati o further increases an increase in activation energy is observed which may be due to the increase in bandgap. The value of sigma(o) indicate s conduction in extended states. (C) 1998 Elsevier Science S.A.